km1h: Re: [AMPS] Parasitics and Blown Filaments

[km1h@juno.com]

--------- Begin forwarded message ----------
From: km1h
To: w8jitom@postoffice.worldnet.att.net
Subject: Re: [AMPS] Parasitics and Blown Filaments
Date: Sun, 11 May 1997 11:41:31 PST
Message-ID: <19970511.114404.9671.6.km1h@juno.com>
References: <19970508123040.AAE19391@fred>


On Thu, 8 May 1997 08:34:46 +0000 w8jitom@postoffice.worldnet.att.net
writes:
>Hi Carl,
>
>You must have misread my comments.

If I did I apologize Tom; sorry for the late reply, been away for several
days.


>> Blown filaments are absolutely possible due to an internal tube 
>failure.
>> Consider the failure a parasitic, gas, lousy assembly, etc. Any one 
>of
>> those can do it. 
>
>Parasitics are not a cause of blown filaments, but mechanical 
>construction sure is...as is mechanical shock.

Parasatics CAN be one of the causes of a filament failure. I never said
it was the ONLY failure mode and you are the one now massaging my
intented statement. 

>My opinion is people who blame all these amplifier failures on 
>parasitic are looking for a single explaination for multiple causes. 

I agree here; there are multiple failure mechanisms involved:
- Parasitics
- Poor circuit design
- Defective Tube
- Operator error
Those are just  a few.
 
>It makes them look like they "know all the answers" because they can 
>give an answer point blank no matter what the problem. 
>No one can disprove the answer without long technical explainations 
>that go beyond the grasp of most neophytes, so they feel relatively 
>safe with the tall tale of parasitics. 
>
>> A case in point is the huge number of Svetlana 572B's with blown 
>filament
>> failures....I had a least 2 dozen happen to me and my customers. Put 
>them
>> in a known stable amp such as a SB-200, turn it on and everything 
>looked
>> fine. Key the relay with NO DRIVE and "Bang".  Svetlana has 
>acknowledged
>> the stability problem and has redesigned the tube. It was an 
>acknowledged
>> parasitic problem based upon internal geometry, not gas or poor
>> construction. 
>
>I have a pile of Sevtlana 572B's here and they FAIL HV breakdown 
>tests. Almost 25 %  arc at just over 3000 volts anode voltage. 
>
>The peak anode operating voltage easily exceeds 4 kV in the SB-200. 

The unloaded DC voltage in a SB200 is ~2500VDC. If it was a HV breakdown
they would have blown immediately. But as I stated previously, the
failure was only after keying the relay without RF drive. There was no
sign of a problem prior to that...even with 30 minutes of standby. 

>You must have talked to a real expert, since Svetlata employs off the 
>street sales people with little or no vacuuum tube experience. Of 
>course, you might have called Russia and talked to a real engineer.

I called Huntsville and was told by a salesperson. What ever their VT
experience has to do with it I dont know. They were just relaying info
from higher-ups. Are you now including sales people in your "knock-em"
list?  


>Anyway, put a typical older Svetlana 572 in a SB-200, and 
>it's Russian roulette. 
>   
>> I feel that Tom's response is irresponsible and is strictly a
>> MFJ/Ameritron CYA  smoke screen. 
>
>That's bunk and you know it. People fall back on personal attacks (in 
>particular you and a certain AG6) when they run out of technical 
>facts. If you can't impeach the data, attack the person responding as 
>dishonst.

Thats NOT bunk Tom; I dont believe that you understand the difference
between criticism and a personal attack.  Many times I fully agree with
you and tell you so. But other times I feel you are wrong, biased or just
plain stubbron.
I have no intention of fueling the ongoing war that you and Rich had
started elsewhere and brought to this reflector.  I have replied with
both praise and criticism to both of you; I just called them the way I
see it.  
Info on this list has taught me a lot; I also hope that I have helped a
few along the way. 
This reflector offers fertile ground for discussions and sometimes they
get a bit warm; no big deal IMO.  I would rather see a good argument that
we all learn from. What annoys me the most are comments from fringe
lurkers who contribute nothing to any technical discussion but are always
telling people how to act. 
  
>> My congratulations to Svetlana for not only quickly responding to 
>the
>> problem but also admitting the reason. Eimac, etc could learn a 
>lesson
>> about customer relations. 
 
>Maybe instead of a personal editorial, you could explain to everyone 
>HOW a parasitic causes a filament to open and roll around in the 
>bottom of the tube.

I wouldnt have a clue, I am not a tube engineer; are you?? I had a
problem and reported it. They responded by both admitting to it and
offering a cure. That is all I expect...not a lot of  hyperbole and smoke
screens crafted to divert from the subject.

>
>I turned on my reading lamp last night. The filament popped. Was that 
>a parasitic?

Was it new out of the box?  What does the warranty card say?  Call your
incandescent engineer and ask him to post a reply. 

73....Carl   KM1H

>73 Tom 

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